Codominance Calculator
Model genetic crosses where both alleles are simultaneously and fully expressed in the heterozygote. Classic examples include Roan coat color in cattle and ABO blood types.
Parental Genotypes
Select the genotype for both parents using alleles CR (Red) and CW (White).
Codominant 2×2 Grid
| CR | CW | |
|---|---|---|
| CR | CRCR | CRCW |
| CW | CRCW | CWCW |
Trait Probabilities
Genotype Ratio
Phenotype Ratio (Both Expressed)
Co-Expression Principle
In codominance, the heterozygous genotype has a unique phenotype representing co-expression (e.g. Roan has both red and white hairs), rather than a mixture or blending.
Codominant Crosses Reference Table (Roan Cattle Example)
| Parental Cross | Offspring Genotypes | Red Phenotype % | Roan Phenotype % | White Phenotype % |
|---|---|---|---|---|
| Red × White (CʳCʳ × CʷCʷ) | 100% CʳCʷ | 0% | 100% | 0% |
| Roan × Roan (CʳCʷ × CʳCʷ) | 25% CʳCʳ, 50% CʳCʷ, 25% CʷCʷ | 25% | 50% | 25% |
| Roan × Red (CʳCʷ × CʳCʳ) | 50% CʳCʳ, 50% CʳCʷ | 50% | 50% | 0% |
| Roan × White (CʳCʷ × CʷCʷ) | 50% CʳCʷ, 50% CʷCʷ | 0% | 50% | 50% |
Calculation Methodology & Biological Principles
Molecular Co-Expression
In codominant systems, both functional alleles produce distinct gene products (enzymes or cell surface proteins) independently without interference.
1:2:1 Genotypic & Phenotypic Equivalence
Because every genotype produces a distinct phenotype, crossing two codominant heterozygotes yields identical 1:2:1 genotypic and phenotypic ratios.
Frequently Asked Questions
What is Codominance? ▼
Codominance is a genetic inheritance pattern where two different alleles at a locus are fully and simultaneously expressed in the heterozygous offspring, without masking each other or blending.
How is Codominance different from Incomplete Dominance? ▼
In codominance, both parental traits appear distinct and simultaneous in the heterozygote (e.g., Roan coat with distinct red and white hairs). In incomplete dominance, the traits blend together to form an intermediate phenotype (e.g., red and white flowers yielding pink flowers).
What are common real-world examples of Codominance? ▼
Classic examples include ABO blood group inheritance (where I^A and I^B alleles are codominant, producing AB blood type), sickle cell trait (Hb^A Hb^S), and coat colors in cattle and horses (Roan).
Related Calculators
View All Biology Tools →Punnett Square Calculator
Generate custom 2x2 Punnett squares and calculate genotype probabilities.
Incomplete Dominance Calculator
Analyze intermediate blended phenotypes of offspring.
Blood Type / Genotype Calculator
Analyze ABO blood group inheritance and offspring probabilities.